The invention described herein relates to a self-propelled lift truck which utilizes a telescopic boom system, particularly intended for raising loads up to considerable height. A typical application is that of moving materials about on building sites, especially where brick-built or prefabricated and/or cast-in-situ concrete industrial buildings are being erected, but the truck finds usefulness in the widest imaginable range of industrial and agricultural sectors wherever general lifting, handling and warehousing requirements prevail.
Essential features of lift trucks to which the `high lift` name is commonly applied are basically the following:
ability to bring a load up to considerable height off the ground--at least 30 ft up; PA0 generous outreach, or forward reach in this instance, permitting of horizontal extension of the load to a notable distance-forward, with respect to the truck's own foremost frontal plane (generally accepted as being the vertical plane lying tangential to the foremost edge of the front wheels); PA0 compactness in the folded-down state, or more exactly, a design envisaging fold-down within acceptable limits which enable the truck's being manoeuvered easily, as well as permitting entry into tight areas walled-in and roofed in such a way as to inhibit easy access; PA0 simple, easy-to-operate controls working the entire vehicle-and-lifting gear; PA0 low production cost. PA0 a first telescopic boom-assembly whose bottom end is hinged to a mounting at the truck-chassis, permitting of rotation about a horizontal axis; PA0 means by which to rotate said first boom-assembly from lowered, all-but horizontal position, into raised position, and viceversa; PA0 a second telescopic boom-assembly whose rear end is fixed immovably to the top end of said first telescopic boom-assembly such that their longitudinal axes create an unvarying angle instrumental in causing said second boom-assembly to lie practically horizontal whenever said first boom-assembly is in raised position; said second boom-assembly projecting forward along the longitudinal axis of the truck with the first boomassembly thus raised; PA0 means for producing the extension of said second boom assembly; and PA0 a lifting-attachment fitted to the forward end of said second boom-assembly .
Of known high lift trucks, a first type used in the past incorporates two or more booms of unvarying length articulating one with the next via horizontally-disposed hinges and caused to rotate thus by hydraulic actuators. This particular design is by now obsolete to all intents and purposes, since height and forward reach could never be of a great order due to the machine's being incapable of a compact fold-down to within acceptable limits.
A second type--more modern, and still in widespread use after a number of years--has a telescopic boom (most commonly, two-stage) hinged at the bottom end to the truck chassis and fitted at the top end with an appliance or attachment which carries the load--normally taking the shape of forks which slip in between the wooden laths of a loading-pallet. The attachment itself is hung-out at a short distance from the topmost end of the telescopic boom, remaining thus cantilivered during operation. Despite the improvement, this embodiment of the lift truck has the drawback of offering a limited forward reach at medium and maximum lift heights, and what is more, horizontal penetration is lacking when obstacles are encountered at such heights--that is, the load cannot be extended to any reasonable distance beyond the forward edge offered by said obstacle--were it to be, for instance, the point where the facing wall of a building meets with the horizontal surface onto which the load must be set down--since the telescopic boom itself would come up against such an edge when traveling forward. Likewise, if one has scaffolding erected alongside the wall of a building, the `obstacle` is brought forward even further, making it totally impossible to set down a load on the building beyond the scaffolding. Another drawback with this type of truck is that pick-up and set-down utilizing forks involves back-and-forward movement of the entire truck--prime mover and boom alike--so as to slide the forks in and out of the pallet on which the load is positioned. This is a `necessary evil` which, in itself imprecise, rough and ready, and jerky, becomes even more of a setback if the ground is uneven or unstable (invariably the case on a building site) and the danger arises of tipping-over altogether when handling a load at considerable height. Again, this particular truck is (almost without exception) incapable of picking-up and setting down from and onto excavated surfaces lying below the level of the ground on which its own drive-wheels happen to sit.
A third type of high lift truck still in widespread use utilizes a telescopic boom hinged at the bottom end to the truck chassis and designed to traverse back-and-forth bodily along tracks and relative mountings fitted to the chassis--also known as a `boom-carriage`. This embodiment also incorporates a carrying-attachment hung out from the end of the boom topmost.
This third type of lift truck has the advantage of longer forward reach at medium and maximum height with respect to type 2, and an additional plus-factor is that no movement of the prime mover is required in order to slide forks in and out of the pallet when picking-up and setting down--this duly being accomplished by the boom carriage arrangement which travels back and forth whilst the truck remains at standstill.
This notwithstanding, the same drawbacks as arise with type 2 as regards horizontal penetration are also encountered here--i.e., when working at medium/maximum height, the boom will surely come up against obstacles projecting outward from the position aimed-at, when moving forward towards said position. A further drawback relating specifically to this type 3 truck is, that when moving the boom-carriage forward with boom, attachment and load consequently being displaced, the center of gravity itself is displaced forward--obliging the operator to lessen the single weights lifted if tipping-over is to be avoided. Furthermore, the boom-carriage design involves a more complex boom-mounting structure, such as renders the whole unit heavier and more costly. Finally, this type of truck is practically incapable of picking-up and setting-down at below ground-level, in the same way as type 2 as aforedescribed.
The object of the invention as described herein is that of overcoming all the drawbacks thus mentioned, improving and widening the scope of performance offered by this type of lift truck as a result.
In particular, the truck to which the invention relates offers a notable degree of penetration in the horizontal, reaching forward well beyond obstacles at medium and maximum working height, as well as at low level. This means, for instance, that a load can be set down comfortably on one of the upper floors of a building even though scaffolding may be erected, or some other such obstruction any how positioned, in such a way as to bring the obstacle to be cleared even further forward than would normally be the case. Better still, the high lift truck described herein can actually leapfrog such obstacles--that is to say, it can spot at points on a lower level than that presented by obstacles at medium and low working heights; for instance, setting-down or picking-up through a window-opening onto/from a floor lying below the level of the actual windowsill.
The lift truck described herein also possesses a considerable reach at medium to maximum working height, which is an indispensable operating characteristic when transferring loads from and to buildings where approach close-in is denied by low obstacles such as excavations or heaps of rubble, planted directly in the truck's path.
The truck as described herein is also capable of spotting on excavated surfaces lying six feet or more below the ground level negotiated by its own wheels.
Moreover, the truck to which the invention relates will slide its lifting-fork attachment in and out of a loading-pallet with both prime-mover and part of the boom at a complete standstill, rendering such manoeuvers swifter, sweeter, more precise, and free of any danger presented by the risk of tip-over.
As compared with truck type 3 aforedescribed, the truck to which the invention relates has increased lift-capacity, whilst affording a less complex, lighter and less costly type of construction in general terms; and all the advantages thus described are obtained without in any way sacrificing other performance features--viz, generous lift height, compact fold-down, ease-of-control, and low production costs.